Syntax

Parameters

Return value

Error codes

The following error codes can be retrieved by the glGetError function.

Name

Meaning

GL_INVALID_VALUE

width was less than or equal to zero.

GL_INVALID_OPERATION

The function was called between a call to glBegin and the corresponding call to glEnd.

Error codes

The following error codes can be retrieved by the glGetError function.

Name

Meaning

GL_INVALID_VALUE

width was less than or equal to zero.

GL_INVALID_OPERATION

The function was called between a call to glBegin and the corresponding call to glEnd.

Remarks

The glLineWidth function specifies the rasterized width of both aliased and antialiased lines. Using a line width other than 1.0 has different effects, depending on whether line antialiasing is enabled. Line antialiasing is controlled by calling glEnable and glDisable with argument GL_LINE_SMOOTH.

If line antialiasing is disabled, the actual width is determined by rounding the supplied width to the nearest integer. (If the rounding results in the value 0.0, it is as if the line width were 1.0) If | Δ x | ≥ | Δ y |, i pixels are filled in each column that is rasterized, where i is the rounded value of width. Otherwise, i pixels are filled in each row that is rasterized.

If antialiasing is enabled, line rasterization produces a fragment for each pixel square that intersects the region lying within the rectangle having width equal to the current line width, length equal to the actual length of the line, and centered on the mathematical line segment. The coverage value for each fragment is the window coordinate area of the intersection of the rectangular region with the corresponding pixel square. This value is saved and used in the final rasterization step.

Not all widths can be supported when line antialiasing is enabled. If an unsupported width is requested, the nearest supported width is used. Only width 1.0 is guaranteed to be supported; others depend on the implementation. The range of supported widths and the size difference between supported widths within the range can be queried by calling glGet with arguments GL_LINE_WIDTH_RANGE and GL_LINE_WIDTH_GRANULARITY.

The line width specified by glLineWidth is always returned when GL_LINE_WIDTH is queried. Clamping and rounding for aliased and antialiased lines have no effect on the specified value.

Non-antialiased line width may be clamped to an implementation-dependent maximum. Although this maximum cannot be queried, it must be no less than the maximum value for antialiased lines, rounded to the nearest integer value.